Any
plant that blooms at the same time as the honeycrip apple would help to
lure more pollinators to the area and would help pollinate the
honeycrisp apple. These other species do not directly help pollinate
the apple tree. Instead they create a favorable/attractive environment
for pollinators to forage. (More flowers = more pollinators; more
pollinators = more pollination – on all plants).

Honeycrisp
apples do need another apple variety in the area to cross pollinate
with to get good fruit set. More pollinators in the area would
definitely help with that cross pollination, but there needs to be
another apple cultivar in the area. The link below is a list of apples
that can be grown in Iowa. Any of the apples with the same bloom time
as honeycrisp (mid-season) could be used for cross pollination. Be sure
that apple tree is within 50-100 feet – this could also be a neighbors
apple or crabapple if it blooms at the same time.

https://yardandgarden.extension.iastate.edu/how-to/apple-varieties-and-their-uses

Some
shrubs that typically bloom around the same time as a honeycrisp apple
and therefore would attract more pollinators to the area, are listed
below.

• Red chokeberry (Aronia arbutifolia)
• Dwarf fothergilla (Fothergilla gardenii)
• Pink Princess Weigela (Weigela florida ‘Pink Princess’)
• Common lilac (Syringa vulgaris)
• Persian lilac (Syringa × persica)
• Redbud (Cercis canadensis)
• Wayfaringtree Viburnum (Viburnum lantana)

The
bloom time every year may not align, but in general these plants bloom
around the same time. Some of them in the list are wider than 5 feet,
but they may have narrow cultivars available (or you may have another
location you can put one).